The present disclosure relates to data storage media and in particular to the detection of defects on data storage media.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Magnetic recording systems store data on a magnetic medium so that the information can be subsequently retrieved. Defect events are not uncommon in hard disk drive (HDD) systems. To achieve low error rates, data can be written at a low density such that each transition in the patterns of magnetization recorded (written) on the magnetic medium results in a strong voltage from the read head which is localized to that particular transition, allowing for recovery of the information using conventional peak detection. However, there is also a conflicting goal of storing as much information as possible on the magnetic medium, which can be achieved by increasing the density but at the cost of increasing error rates.
Defects typically occur in bursts; i.e., groups of consecutive bits/symbols in a given sector (or block, or codeword). While long bursts (e.g., 50 bits or longer) are generally easier to detect, short bursts are typically much more difficult. One of the most difficult classes of burst errors to detect is the occurrence of several short bursts in a single sector.
The difficulty lies in setting the parameters of a detector so that short burst defects can be detected with a low probability of missing a defect, while at the same time avoiding having too many false alarms. For example, a detector that is configured to provide near-100% accuracy in detecting defect locations on the storage medium is likely to also trigger a very large number of false alarms, namely the flagging of non-defect bits as defects. Such types of burst errors are especially detrimental in iterative decoder systems, which are widely used in disk storage devices.
These and other issues are addressed by embodiments of the present disclosure, individually and collectively.